1. Technical Field
The field of the invention is mobile communications and, more particularly, to signalling used therein, for instance in the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) of the Third Generation Partnership Project (3GPP) and beyond.
2. Discussion of Related Art
In further evolution of mobile communications, for example, in the WCDMA (Wideband Code Division Multiple Access) system, all services could be implemented with HSDPA (High Speed Downlink Packet Access)/HSUPA (High Speed Uplink Packet Access) (including real time (RT) services which uses a very short duration frame (transmission time interval or TTI)). Also, traditionally circuit-switched services are moving into the packet-switched domain. Although disclosed in the context of the current mobile communications environment, the present invention is not limited thereto but should be broadly seen as applicable to future evolution thereof as well.
Even though only one frequency need be used, a UMTS operator has multiple 5 MHz frequency blocks available for implementing packet-switched services in the WCDMA system. It is foreseen that different numbers of DL and UL carriers may be in use simultaneously to meet potentially asymmetric capacity needs.
Spectrum efficiency and flexible use of available spectrum will be elements of cost efficient future solutions. Efficient usage of available radio resources in the DL direction requires fast and dynamic allocation of DL carriers to different users when multiple DL carriers are available in a system. The current WCDMA deployment plans do not provide a signalling scheme/signal structure to enable fast allocation of HSDPA carriers from a pool of multiple DL carriers. WCDMA has not had multi-carrier solutions so far.
If new features are to be introduced to HSDPA (for example, the above-mentioned multicarrier, MIMO (multiple input multiple output) or additional new services such as voice over internet protocol (VoIP)), it may be that new parameters will have to be signalled (e.g., the carrier frequency in multicarrier system, stream identification or other stream specific parameters in case of multi-stream MIMO) or it may be that not all parameters or not the whole range of those parameters as presently specified may be needed (e.g., with VoIP larger transport block sizes are never used due to the low data rate). Then it could be necessary to change the frame structure of the signalling channel (HS-SCCH) in order to be able to signal the new parameters or to signal the existing parameters more reliably (e.g., if the transport block size (TBS) field were to be shortened for VoIP, more channel coding would be possible).
The HS-SCCH is used to signal parameters of the high speed data shared channel (HS-DSCH). One of the major parameters is the user equipment identifier (UE ID) which indicates which user equipment should decode the HS-DSCH. Currently only one UE ID is allocated per user equipment (according to the current specifications). The parameters and the frame structure of the HS-SCCH is fixed.
The existing structure of the HS-SCCH (High Speed Shared Control Channel) is specified for HSDPA in TS 25.211 and TS 25.212 of the 3GPP WCDMA specification, where a number of bit fields are reserved for signalling to the UE. See, for example, Section 4.6 of 3GPP TS 25.212 V 6.4.0 (2005-03). However, because of the above-mentioned evolution, in later releases of WCDMA there may arise a need to indicate different information to the UE receiving data on HS-PDSCH (High Speed Physical Downlink Shared Channel), or the UE may need to receive multiple HS-DSCH (High Speed Downlink Shared Channel) sessions simultaneously from the BS (Base Station (called Node B in 3GPP)) MAC (Medium Access Control). There is currently no room in the HS-SCCH signalling structure as defined in the 3GPP specifications to indicate the frequency carrier or some other new L1/MAC parameters that may be needed or possible.
If the problem were merely that the user equipment only needs to receive a new set of parameters, then this could be informed to the user equipment by RRC signaling. Then the UE would be able to receive parameters as it currently does but assuming a different frame structure. If, however, the UE needs to receive multiple services, then the UE may need to receive multiple HS-SCCH frame structures or formats depending on the service or some other factor. There is no mechanism to tell the UE which HS-SCCH frame structure (i.e., which parameters are signal, what is there value range and how they are channel encoded, etc.) is being used in a given transmission time interval (TTI).
Provisioning for more efficient use of DL (downlink) signalling resources could be achieved by providing some new, different HS-SCCH structures for DL HSDPA signalling. For example, for some transmissions on HS-PDSCH not all the specified fields are needed, potentially new signalling could be added, or a smaller number of bits would be enough for some of the currently existing HS-SCCH fields. Specifying another HS-SCCH structure in a later release of the 3GPP specifications is possible, but this would have to be a different HS-SCCH with redesigned coding, puncturing, error detection, etc. Just adding a new HS-SCCH to the system also brings the problem of the UE knowing which HS-SCCH structure it is to receive with. On the other hand, as suggested above, there may be multiple reasons for introducing new signalling structures in WCDMA, such as VoIP services and so on.
In view of the fact that HSDPA will be widely deployed for packet switched traffic in the near future and the need for enhancements of HSDPA, along with enhancements for the signalling, such as some new L1/MAC parameters, there would naturally be a desire to avoid changes to the high speed shared control channel (HS-SCCH). The present invention proposes how these new parameters could be signalled without changing the HS-SCCH structure or how the existing HS-SCCH signalling could be adapted to perform signalling using different signalling structure in a backwards compatible way, i.e., so as to be consistent with the existing HS-SCCH structure.
The problem has not been solved earlier. It should be noted again that this invention is not specifically confined to multicarrier WCDMA or VoIP.